A problem with the software for Garmin's GTX 330 and GTX 330D Mode S transponders has prompted the FAA to propose an airworthiness directive (AD) to fix the problem. But Garmin has told AOPA that it has already sent updated software to fix the problem to all Garmin Aviation Service Centers.

Without Garmin's recently released software 3.03, the Mode S transponders may not reply to Traffic Collision Avoidance System (TCAS) interrogations from other airborne traffic detection systems. That could cause the "safety net" of TCAS/Transponder operations to fail, thereby increasing the risk of a possible close call or mid air collision.

Garmin issued a Safety Bulletin in mid-2003, and has since shipped the upgraded software to all of its service centers.

"Garmin is offering to pay for both the software upgrade and the avionics shop time to install the upgrade," said AOPA Manager of Regulatory and Certification Affairs Rob Hackman. "The company tells AOPA that many of its aviation service centers have already updated their customers' transponders."

Anyone with affected equipment who has not received the software upgrade should contact Garmin International Inc., 1200 East 151st Street, Olathe, KS 66062, 913-397-8200. If eventually published, the AD could officially impact up to 1300 aircraft, although most owners are likely to have complied before that happens.

FMI: www.garmin.com, www.faa.gov